As shown in FIG. 1, an auto fine tuning device employed in a conventional television or a VCR includes a remote control signal receiving part 2 for receiving transmission signals from a remote controller, a key pad 3 for applying operation orders according to user input through keys, a microcomputer 1 for controlling tuning to a broadcasting signal by transmitting tuning data in response to the signals received from the remote control signal receiving part 2 and the key pad 3 and transmitting designated control signals for generation of OSD letters, a tuner 4 for transmitting a broadcasting signal of a selected channel of the signals received through an antenna ANT under the control of the microcomputer 1, an intermediate frequency signal processing part 5 for processing the output signal of the tuner 4 into an intermediate frequency signal and transmitting a synchronization signal of the broadcasting signal and an auto fine tuning signal(hereinafter called `AFT`) to the microcomputer 1, a video signal processing part 6 for processing an video signal received from the intermediate frequency signal processing part 5, an audio signal processing part 9 for processing an audio signal received from the intermediate frequency signal processing part 5, an OSD character generation part 7 for transmitting OSD characters in response to the control signal received from the microcomputer 1, and a synthesizing part 8 for synthesizing the video signals received from the video signal processing part 6 and the OSD characters received from the OSD character generation part 7 and transmitting the synthesized signals to a color picture tube CPT.
Operation of the convention auto fine tuning device described above is explained below.
When a user, by pressing the buttons on the remote controller, transmits a channel selection to the remote control signal receiving part 2, or by pressing the keys on the key pad 3, transmits a channel selection to the microcomputer 1, the microcomputer 1, transmits channel tuning data to the tuner 4. The tuner 4 detects the signal of the selected channel from the broadcasting signals received through the antenna and transmits the detected signal to the intermediate frequency signal processing part 5.
The broadcasting signal received from the tuner 4 is processed into an intermediate frequency signal, detected as a synchronization signal and AFT signal at the intermediate frequency signal processing part 5.
Upon reception of the detected synchronization signal and the AFT signal, the microcomputer 1 determines the broadcasting signal of the selected channel tuned to the received synchronization signal, and according to the result of the determination, transmits tuning data to the tuner 4 to carry out fine tuning.
The broadcasting signal selected through the foregoing process is processed into an intermediate frequency signal at the intermediate frequency signal processing part 5, and the video signal and the audio signal received from the intermediate frequency signal processing part 5 are transmitted to the video signal processing part 6 and the audio signal processing part 9, respectively.
The audio signal, processed at the audio signal processing part 9 is, transmitted to a speaker, and the video signal is processed into an image at the video signal processing part 6 synthesized at the synthesizing part 8 with the OSD character signal received from the OSD character generation part 7 under control of the microcomputer 1, and displayed on a color picture tube CPT.
The conventional fine tuning device has problems in that the convention fine tuning device has difficulty in exactly distinguishing the tuning data of a center frequency from the synchronization signal received according to the phase locked loop data at the time of initial channel tuning. In particular, the conventional fine tuning device cannot exactly tune in the broadcasting signal when the AFT signal level has been mistuned even though the broadcasting signal has been detected at search time, due to processing of the synchronization signal determination at the intermediate frequency signal processing part 5 at the time of initial tuning, i.e., at search time of search.